Tritium is a radioactive isotope of hydrogen. Because it is relatively weakly radioactive, it is generally not considered dangerous externally. However, if concentrations are too high, it can be dangerous if inhaled or ingested. In some cases, the main concern is tritium water vapour in the air. In other cases, both tritium gas and tritium water may be of concern. Thus, tritium-in-air detectors have been designed to monitor the levels of tritium in the air that may be inhaled.
Prior art detectors deal with the problems created by background Gamma radiation, and beta radiation (which comes from noble gases in the air). Because the signal from tritium—even from dangerous levels of tritium—can be very low relative to gamma and beta radiation, existing devices include features to compensate for these other types of radiation. For example, in a 1-liter ion chamber, the sensitivity of tritium is 1 fA (femto Apmere, which is 1×10−15 Amperes). The Gamma background signal, which is non-uniform, could be 1100 fA, while the beta radiation background signal could be 3000 fA. Thus, prior art devices were designed with quadruple ion chambers to provide high gamma compensation. Noble gas compensation is achieved by injecting dry air into the compensation chambers. Examples of existing prior art detectors which have some or all of these features are the Overhoff Technology Corporation Model 400S BDγC detector, and the Tyne Engineering Model 7043 detector.
The Overhoff detector uses quadruple ion chambers that are separate and made up of square metal cups. The shell of the measuring pair of ion chambers is connected to a negative battery terminal and the shell of the compensation pair of ion chambers is connected to a positive battery terminal. All four central rods from each of the four ion chambers are connected together. Ideally, the positive charge from the measuring chambers is equal to the negative charge from the compensation chambers caused by Gamma and beta background radiation.
The Tyne detector consists of quadruple ion chambers made of separate cylindrical tubes fastened together for low tritium range and a small central tube for high tritium range. All shells of the tubes are connected together electrically to the negative terminal of a battery. Each central rod of each chamber is connected to a pre-amplifier to convert electrical charge to voltage. The four voltage signals coming from the pre-amplifier are fed to a computer to do Gamma compensation, beta radiation compensation and tritium signal processing.